First of all this is not really a MM problem, this is something that you should address with your Basis guys. They have authority to execute transactions to analyze where the program spends its time.

In general you always have to ask yourself what you are actually wanting from the system. This program has a selection screen, if you execute it without doing any selection then the program has to read everything which takes obviously longer for some hundred thousand vendors than for 50. You have not mentioned what you entered and you have not given any indication how much vendors you have in total to allow a stranger to make a judgement.

the change document tables that are read with this report are usually among the biggest tables in a SAP system, as it stores all changes from all business transactions.